Two decades ago a demon infestation changed the way we play games. Doom was first launched 20 years ago today, and while it wasn't the first game to let you play from a first-person perspective, it was the game that ushered the FPS genre into the mass consciousness. Today the likes of Halo and Call of Duty dominate sales charts, but it wasn't until Doom that people really saw the potential of a 3D game played from a first-person point of view — and that changed the kinds of games people started making.

"The genre of FPS is probably the most important thing that happened with Doom," says lead programmer and id Software co-founder John Carmack. "Probably even broader, though, is all of the people that Doom influenced — how many people decided that, after they saw this, they wanted to do something like this."